Going Off-Grid with Solar:
A Solar Power Rocks Guide

Shedding the complications of modern life doesn’t mean you have to live like an ape in the wild. With solar power and modern batteries, you can live like royalty in the outback.

A big part of our mission is to turn your dreams of solar power for your home into reality. That includes any home, anywhere. This is your ultimate guide to electrifying your off-grid house with the sun. Congratulations on finding it!

You may want to bookmark this page, because we don’t imagine you’re going to get through it all at once.

What do we mean by “off-grid”?

Unless you want to live like a wild person, taking a tiny house off the grid requires heat and electricity. Combining a solar panel system with propane for heating and cooking can meet almost any need for comfort and self-reliance. All you need is a source of clean water and propane tank refills.

What if I don’t have a tiny house?

We geared this guide toward tiny house owners, because there are a lot of people out there interested in this type of living without a lot of good information out there about how to go about it. If you’re planning for a more robust off-grid setup, the tools we outline in this guide can work for you, too!

If you’re planning for a bigger off-grid home, you’ll have more options, because your space will be less limited. With a larger roof or a shade-free south-facing area, you could install enough solar to power the same appliances you might find in any on-grid home.

Chapter 2:
Planning to go off-grid

Know what you need

Off-grid electrical systems can be as small as a solar panel plugged into one of those battery backups with outlets on them. That might only cost a couple hundred bucks, but it’ll only provide enough power to charge a laptop and run a light bulb. If you want to run more typical home electrical loads on solar energy, you’ll need a more legit system.

A more robust system will include multiple solar panels, a battery bank monitored by a charge controller, and an inverter to turn the DC solar electricity into AC electricity useful for running appliances.

The next section helps you learn what all the parts are, how they work together, and the reasons to choose certain components over others. Since you’re unique, your home is too. Designing your solar system won’t be a simple one-size-fits-all proposition.

There are three important questions you need to ask yourself before you begin this journey:

How much electricity do you need (sub-question: how long could you go without sun)?

How much space do you have available?

What’s your budget?

When it comes to tiny houses, the answers to those questions is usually the same: “not very much!” Tiny houses all have to fit into relatively the same size and shape, because moving them requires they be legal for transport. That means they’re small and use efficient appliances. It also means it’s a little easier to come up with a basic solar system outline.

Let’s answer those three questions now:

Question 1: How much electricity do you need?

This question is tricky because it can have multiple meanings depending on your interpretation of the word “need”. In going off-grid, it’s necessary to strip away some conveniences to make sure you have only what you “need”, but whether that means “what you need to survive” or “what you need to be comfortable” is up to you.

It’s your life, and this question is the first step toward designing it how you want it to be.

When it comes to solar specifically, this question is about making a list of every appliance you’ll use on a day-to-day basis, and defining the minimum amount of electricity you’ll want during the darkest time of year. The answer will determine a great deal about your off-grid solar system: how many panels you need, how big your batteries have to be in case you don’t get sun for a few days, and how much the whole thing will cost.

In some cases, you’ll discover that solar isn’t practical for your needs, or that it can only meet some. If that happens to you, you’ll have to pare down your needs or make another plan.

Sound a little intense? It can be. Don’t worry. You don’t need to jump in with both feet right away, and we’ve got you covered with an easy-to-use calculator down the page a bit.

On to the next question:

Question 2: How much space do you have available?

If you own a tiny house, you know space is at a premium. Adding a solar system is great for autonomy, but the solar panels, batteries and other stuff you need does take up space.

If you need a lot of electricity every day, you might be limited by the space you have. The answer to this question will determine whether your tiny house can hold a solar system big enough to meet your needs, and whether the batteries you’ll need will fit, too.

It’s a good idea to gather some information about your space as you prepare to design an off-grid solar system. You’ll need roof space for panels, a warm (but not too warm) ventilated spot for batteries, and an outside wall where you can put electrical equipment.

Up on the roof

The first thing to do is measure your roof space. If you have a roof with a peak in the center, you’ll want to measure only one side. Solar panels work best if they’re pointed south during the day, so only one side of a gable or gambrel-style roof will get panels.

Storage for your storage

Batteries take up space, too; about 1 square foot per battery, and 15-20 inches high. The ideal place is somewhere the batteries can stay about room temperature, with ventilation for fumes if you choose standard Flooded Lead Acid (FLA) batteries. You could choose lithium batteries if you don’t have a lot of space, but then you’d be spending 4-5 times as much.

Meet me outside

As for the other equipment, you’ll need a large electrical box (about 3 feet wide, 4 feet high, and a foot or more deep), which will hold all the stuff that gets power from your panels to your batteries and into your house. People generally mount these in an enclosure on the outside of their tiny house, above the trailer tongue (between the trailer hitch and the outer wall of the house). Do you have space there?

Question 3: What’s your budget?

Ah, the perennial question: how much can you afford to spend? Again, your answer to this question may limit your options.

That single solar panel with a battery box might cost $500-$1,000, but for the robust system we described above, you can expect to spend between $6,000 and $10,000 for a solid system.

Chapter 3 includes an outline of a typical off-grid tiny house solar system, complete with the costs for components.

Chapter 3:
A typical tiny house solar system

Most tiny houses are about 8 feet wide and 20 to 28 feet long. For this size, we recommend a simple solar panel system with batteries that can provide enough power for most people’s needs. With efficient appliances and propane cooking, 4 solar panels charging 8 batteries can provide all the energy you need, for as cheap as $7,500 before the federal solar tax credit.

If you’ve already got your tiny home wired for AC electricity, here’s what goes into making a tiny-house solar system:

Sample system

4 Canadian Solar 275-watt solar panels

make the electricity you need$650
(each additional panel about $165)

4 IronRidge XR100 Roof Rack Kits with FlashFoot Mounts

hold the panels to the roof$250

Pre-wired inverter panel

charges batteries and turns solar power into home power$4,000

Wiring for Panels and Batteries

gets electricity where it needs to go$400

8 Trojan J305P-AC 6V Batteries

store the power you need for times when the sun isn’t shining$2,200

Total system price:

$7,500

What you get from the above set-up

The system we describe above can produce enough power to run a refrigerator and a mini-split heating and cooling system, charge phones and laptops, and keep the lights on. The solar panels will make a about 5 kilowatt-hours of electricity on a sunny day, and the batteries will provide enough juice for 3 days without sun.

On top of that, the system is designed to plug into a backup generator or the grid to avoid letting your batteries run dry and cost you a couple grand. You won’t be sending any solar power to the grid, but plugging in can be really helpful during a cloudy week of winter.

What you should feel comfortable giving up

In addition to the $7,300 leaving your pocket, going off-grid means sacrificing some of the modern conveniences most people enjoy. Basically, any electric appliance that produces heat is out: toasters, hair dryers, microwaves, electric stoves, and more. Instead, your cooking and water heating will be done with propane.

How it all fits together

? ? Well the solar panel’s connected to the charge controller and the charge controller’s connected to the batteries, and the batteries are connected to the inverter, and the power goes to your house. ? ?

Chapter 4:
Designing your system

Ready to take a crack at designing your ideal system? Here’s a quick outline of what we’ll cover in the next section:

Your Solar System

Step 1: Calculate your power needs

Step 2: Calculate your battery needs

Step 3: How much solar?

Step 4: The rest of the system

Step 5: Buying equipment

Step 6: Putting it all together

Here’s where we get into the nitty gritty. You’ll be making a list of all the appliances you use to determine how much energy you need, designing a battery pack to hold the electricity, finding out how many solar panels you’ll need to produce enough to fill those batteries, and finally choosing the equipment that will transmit and transform that power for use in your home.

Okay, ready? It’s time to take the next step toward your new solar system!

Your solar system, Step 1: Calculate your power needs

It’s time to take inventory. This is the single most important step when you’re beginning to consider solar power for your home. The more electricity you need, the bigger your system needs to be. If you need too much, you might just size yourself out of a tiny home.

If you’ve lived in a grid-connected tiny house for a while, you might know exactly how much electricity you use each month, because it’s right there on your electric bill! If that’s the case, great! You can divide your average monthly bill by 30 and get your daily needs that way. But if you’re still in the planning stages, here’s how to plan for your energy needs:

In an electrical system, each thing that requires power is called a “load.” To find out how much power you need, you make a list of all your loads, and multiply their power requirements by how many hours you’ll use them in a typical day.

Here’s how it works:

Make a list of *every* appliance, power tool, and lightbulb you need.

Look at the manual, label, or on the internet to find the power they need to run, measured in watts

Also find the “surge power” they need, measured in watts. You won’t need this information now, but it will come in handy when you’re choosing a DC/AC inverter later.

Multiply the wattage of each appliance by the number of hours you need it.

Some appliances like refrigerators are plugged in all day, but only draw power periodically. We’ve included a handy table below with average wattage and usage per day.

Appliance

Wattage

Hours/day

Watt-Hours/day:

Air Conditioner – 11000 BTU

1,010

5

5,050

Air Conditioner – 13500 BTU

1,800

5

9,000

Air Conditioner – 15000 BTU

2,000

5

10,000

Blender

400

0.5

200

Coffee Maker

600

0.5

300

DVD Player

350

1

350

Electric Grill (tabletop)

1,650

1

1,650

Fan (portable)

40

4

160

Hair Dryer (1600 watts)

1,800

0.5

900

Laptop computer

225

4

900

Lightbulb – 100W Incandescent

100

4

400

Lightbulb – 14W LED

14

4

56

Lightbulb – 18W CFL

18

4

72

Lightbulb – 60W Incandescent

60

4

240

Microwave Oven (650 watts)

1,000

0.5

500

Mini-Split Ductless HVAC

800

5

4,000

Radiant Heater

1,300

4

5,200

Radio

100

2

200

Refrigerator – 17 cu ft

180

6

1,080

Refrigerator – 20 cu ft

200

6

1,200

Satelite Receiver

250

2

500

Slow Cooker

220

3

660

Television – Flat Screen

120

2

240

Television – Tube type

300

2

600

Video Game Console (XBOX)

100

2

200

You could do all this on paper, but why not use this simple calculator to add up your needs:

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Ta-da! Now write that number down, because you’re going to use it later to determine how much battery power you’ll need.

How long can you go without sun?

Solar panels make electricity when it’s sunny, so you need batteries to capture that electricity and store it for later use.

But sometimes the sun hides away for a day or two. So your batteries need to be able to hold enough electricity to power your appliances for a days at a time—the general rule is three days without sun, but two is acceptable, especially if you’ll have a backup generator to charge the batteries.

Multiply the energy you need for one day by the number of days you need to store it. Keep that number for later, when it’s time to design your battery bank.

Your solar system, Step 2: Calculate your battery needs

Batteries are an essential component of an off-grid solar system. You need to be able to have power when the sun isn’t shining, and that sometimes means reserving enough for a few days of stormy or snowy weather.

The good news is, now that you know how much energy you need per day, you can figure out exactly how many batteries you need! Read through the next section to learn about the important variables in the battery bank equation. At the end, we provide another handy calculator that lets you play with the numbers and discover the type of batteries that are best for your off-grid project!

Here’s what you need to know:

The basics: how batteries work

Your batteries have to supply the amount of power you need (in watts) for the length of time you need it (in hours). Combine the two to get watt-hours (Wh).

Remember, watts = volts x amps.

Voltage is to electricity like water pressure is to plumbing. It defines the force of electrons flowing from one place to another.

Amperage is the amount of electricity that can flow.

Battery capacity is measured in how many amp hours (AH) a battery can supply can supply at a given voltage (V). So a 6V battery with a capacity of 100 AH can produce 600 Wh. But 6V is not enough. Going back to the water pressure analogy, it’s like a trickle of water coming out of a hose. We need it to be forceful.

So we’d design a battery bank of 48 V, which would supply 4,800 Wh if it was made up of 100 AH batteries.

Days without solar energy

If your battery system isn’t big enough, you could be without power after just 1 day without sun. Keeping enough batteries for 2 days is usually safer, and 3 is the recommendation if you’re *really serious* about being comfortable.

Going back to the last example, if we wanted 4,800 Wh per day for 3 days, we’d need a 48 V battery bank made up of 300 AH batteries.

Battery Type

There are 3 main kinds of batteries for off-grid purposes: Flooded Lead Acid (FLA), Absorbent Glass Mat (AGM), and Lithium.

FLA batteries are big, heavy and require regular maintenance (checking and adding water to maintain proper electrolyte levels). They’re also the cheapest option, even considering their relatively short lifespan of 2-4 years.

AGM batteries are big, heavy and moderately expensive, but are maintenance-free. They have a lifespan of 3-5 years; maybe a little more with proper care.

Lithium batteries are compact, lightweight, and very expensive, but they’re also maintenance-free, and can potentially last for much longer than other types (8-10 years).

Here’s a table to compare deep-cycle batteries:

Battery Type

Size

Weight

Capacity

Lifespan

Cost

Flooded Lead Acid (FLA)

Large

Heavy

Medium

Short

Low

Absorbent Glass Mat (AGM)

Large

Heavy

Low

Short

Medium

Lithium

Small

Light

High

Long

High

And here’s a diagram showing the relative sizes and weights:

Your budget and available space will dictate your final decision, but for our money, FLA batteries perform just fine, and the maintenance isn’t too onerous. As long as you have the space and can handle the weight, go FLA.

Note: Advances in Lithium batteries are occurring every day, and within 3-5 years, they will be the dominant type of off-grid battery. If you go FLA now, lithium may be your choice when it’s time to replace them.

Depth of discharge

Depth of discharge (DoD) refers to the maximum amount of energy you can draw from a battery without greatly reducing its lifespan. When it comes to FLA and AGM batteries, keeping them charged to more than their ideal DoD can double their lifespan.

DoD is strongly correlated to cost. Cheap FLA batteries should only be discharged to about 50% of their capacity at any given time. That means you have to select batteries that are rated to store at least double what you’ll need for 2 or 3 days, which can mean a lot of batteries.

An average 50% DoD allows FLA batteries to last for 3-4 years (given otherwise ideal conditions). Discharge any more than 50% and you’ll reduce the batteries’ lifespans down to just a year or two.

Some AGM batteries can be discharged up to 80% (though the ideal for most is still 50%), and they should also last 4-5 years. Lithium batteries can be discharged between 80% and 100% without problem.

Since we’re interested in sizing a battery bank to handle multiple days’ of electricity, and you won’t often need to go multiple days without recharging the batteries with solar energy, it is possible that the average DoD of a well-designed solar system could be more like 30%, meaning longer lifespans for every kind of battery.

Sizing your battery bank to provide 3 days of power at a maximum 50% DoD should be adequate to ensure you don’t often discharge the batteries that much. We’ll use that number for the rest of our calculations.

Continuing with out example of above, if we need 4,800 Wh per day for 3 days, that’s 300 AH at 48 volts. But if we on;y want to allow them to discharge to a maximum of 50% after those three days, we’d need double—600 AH of batteries.

Temperature

Deep cycle batteries work best at about room temperature. If they get too cold, the amount of energy they can hold is reduced. Too hot and their lifespan goes down.

Unless you’ll be storing batteries outside in the desert, Cold is the concern here. You need to consider the reduction in capacity that could occur during the winter and size your battery pack to meet the needs of the coldest time you might need them.

Here’s a handy guide to how much bigger your battery bank will need to be at a given temperature:

Temperature
(° Fahrenheit):

Size of system
(# of times larger):

80+

1.00

70

1.04

60

1.11

50

1.19

40

1.30

30

1.40

20

1.59

As you can see, if your batteries will be exposed to cold, you’ll need the bank to be much larger. To prevent against problems, do your best to find a place to store batteries that doesn’t get too cold.

System Voltage

System voltage is important to decide how many batteries you need. Generally speaking, the larger the energy need per day, the higher the voltage. That’s because higher voltage systems allow for greater wattage output.

Another consideration is charging. A single string of eight 6V batteries will make a 48V system. The single string is easy for the charge controller to handle, charging the batteries evenly and maximizing their lifespan.

If instead you have a 24V system with two parallel strings of four 6V batteries, you could end up in a situation where one string charges and discharges at a different rate, potentially reducing the lifespans of its batteries.

We always try to design systems that put out 48 Volts, but 24 can be a good option for tiny houses. 12 Volts is not enough to run tiny house appliances.

Determining your battery needs:

Now that you know the variables, here’s how to put them together to determine how much battery power you need:

Take your watt-hour needs per day (example: 2,000 watt-hours)

Divide by inverter efficiency (about 90% of energy from your batteries will actually make it to your appliances. That means the inverter is 90% efficient)

2,000 / .9 = 2,222

Multiply by number of days you might go without power (ex: 3 days)

2,222 x 3 = 6,666

Divide by depth of discharge (FLA: 50%)

6,666 / .5 = 13,332

Multiply by the temperature effect. (We’re keeping our batteries in a compartment in the house, so the coldest they’ll get is 60 degrees F. Looking at the temperature table above, we see that at 60° F, we’ll need a 1.11-times bigger battery bank):

13,332 x 1.11 = 14,799

Divide by system voltage (You need 14,799 watt-hours. Watts = Volts * Amps. We want to shoot for 1 string of batteries in a 48V system, so we’ll divide by 48 to get the size of battery bank we need, measured in amp-hours):

14,799 / 48V = 308 amp-hours.

You can do the calculations yourself and play around with the numbers to see the possibilities. But don’t write it our by hand—use our calculator! To make things easy, we’ve pre-populated the calc with the number of Wh per day from our example above (but you can change it):

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Choosing batteries

Now that you know how much power you’ll need, it’s time to design a battery bank! Here are the rules for building a bank of batteries:

Batteries are measured in voltage and capacity (amp-hours)

Voltage is to electricity like water pressure is to plumbing. It defines the force of electrons flowing from one place to another. Voltage needs to be high enough to efficiently deliver the energy when it’s needed.

Amperage is the amount of electricity that can flow.

Here’s an example: In the case of “amp hours” (AH), a 6V battery with a 100AH capacity is saying “I can send 100 Amps of current at a pressure of 6 volts for 1 hour.”

Watt-hours = Volts x Amp-Hours

Wiring batteries in series (i.e., a “string”) adds voltage

Wiring batteries in parallel adds amperage

Fewer strings of batteries is better

Here’s a look at series wiring:

Here’s a look at parallel wiring:

Here’s two strings of batteries wired in parallel:

Fewer strings is better

Batteries are charged by a charge controller, which takes solar energy and transfers it to the batteries until their capacity is close to 100%. Because the voltage of one string remains constant as it charges, it’s easy for the charge controller to charge up the batteries.

If two strings are present, the charge controller has to work harder to balance the voltages, and the strings can end up charging at different rates, meaning they will heat differently and their lifespans may be decreased.

Our battery bank example

In our example, we’ve already determined we’ll need 308 amp-hours times 48 volts, or 2,222 watt-hours. We’ll need to purchase eight 6-Volt batteries to create a string of 48 volts. (6 x 8 = 48). In order to meet our needs with a single series-wired string of batteries, we’ll need to find batteries with a capacity of at least 308 amp-hours.

Flooded lead acid batteries generally come in voltages from 2V to 12V. If we were to choose 12V batteries, we’d need one string of 4 batteries (12V x 4 = 48) with at least 308 AH capacity, or two strings of 4 batteries with at least 154 AH capacity.

As a rule, batteries of high capacity (high AH) are more expensive. If the number you ended up with from the battery calculator above is much higher than 400, divide it in 2. You’ll end up with two parallel strings of batteries of half the capacity of your total need.

We’d need 8 of them in series to make a 48V, 330AH battery bank. The completed bank would weigh about 800 lbs. and take up about 6 cubic feet.

Your solar system, Step 3: How much solar?

Just like the needs of your appliances, the output of your solar system is measured in watts. What you need to figure out is how many watts of solar panels you need to produce enough energy to meet your needs and keep your batteries charged.

The limiting factor here is daily sunlight. You need to design your system to produce the right amount of energy, even on a day during the darkest time of the year: winter.

For some people, the answer will be “I’ll park the house somewhere with grid power for the winter” and that’s fine. It could mean you need a smaller solar system! For others, you’ll need those panels to run a heater during January in Minnesota. And don’t forget: no matter where you are, you’ll need a sunny parking spot.

Use our handy calculator to see how you can get the right amount of electricity for the darkest time of year where you are:

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Your solar system, Step 4: The rest of the system

Plan your work, and work your plan. If you buy a kit from one of the reputable suppliers listed below, you’ll get wiring diagrams to show you how to hook everything up. You can probably find a kit that matches the numbers you came up with in steps 1-3 of our guide.

If you’d prefer to buy all the components yourself, you can get exactly what you want, and you might be able to take advantage of sale prices on certain components to bring the costs down.

Controllers, inverters, and breakers, oh my!

Now you know how big your battery bank will be and how many solar panels you need. The next step is to choose the components that hook it all together to get power to your main electrical panel. Here are the major components of the rest of the system:

Mounting racks to attach the panels to your roof

A charge controller that sends energy to and from the batteries

Breakers to isolate other components that isolate parts of the system for installation and maintenance

A DC/AC Inverter to take DC electricity from the solar panels and batteries and turn it into AC energy for use in your tiny house

Wires to connect the panels together, connect the charge controller to the other components, and connect the batteries together to form a bank.

Warning: This is where designing a solar system can get complicated. If you’re not intimately familiar with wiring schematics and electrical equipment, you might find your head spinning. Thankfully, some enterprising companies came up with a solution to your woes: the pre-wired system.

Pre-wired inverter panels make the world go ’round

A pre-wired inverter panel is a combination of all the electrical gear you need to bring power from your panels to your batteries, and on to the main AC electrical panel. The systems come attached to a large metal panel, with all the appliances you need wired up just right.

Here’s an annotated version of one:

This weird giant-robot-looking thing is the brains and superhighway interchange of your whole system. It does everything but make a decent cup of espresso!

The panel is designed and built by experts, and purchasing the components all together like this makes it extremely easy to install off-grid solar. You still have to put panels on your roof and run wires from them to the battery charge controller, you still have to wire up a battery bank and hook it to the other end of the controller, and you still need to run a wire from the inverter to your main panel.

The amount of work saved by purchasing a pre-wired inverter panel is staggering. But you still have some choices to make. The variables include charge controller size, system voltage, and inverter output.

Read on to learn how to make the right decisions for your off-grid project!

Choosing mounting racks:

With mounting racks, you’re basically forced into a choice based on your roof type.

For composite shingle roofs

If you have a traditional composite shingle roof, you will choose mounts with flashing that slides underneath the layer of shingles just above the mounting points, combined with aluminum racks that the panels are attached to.

Here’s a look at how the racking system works:

For standing-seam metal roofs

If you have a standing-seam metal roof, your choice is much easier and nicer. You don’t have to drill into anything, because the mounts can be attached to the seams of your roof with a clamp. The panels can be clipped right to the mounts with a separate piece, eliminating the need for additional racks.

Here’s the metal roof mount in action:

Ground mounts

Ground mounting uses the exact same rails as a roof mount, but the rails are attached to a metal frame installed in the ground instead. Our favorite solar mount manufacturer, IronRidge, makes hardware to attach panels to frames built from 2-inch or 3-inch steel pipe. If you;ve got some extra sunny space near your off-grid house and you’re not going anywhere, ground mounting is an excellent way to fit as many panels as you need without the hassle of drilling into your roof.

Choosing a charge controller:

The charge controller is the electronic brain that helps your batteries charge fully and evenly. They take solar power from your panels and send it to to your battery bank for storage. They also act to send power from your batteries to your inverter for use in your home. There are two main kinds, called PWM (for Pulse Width Modulation) and MPPT (for Maximum Power Point Tracking).

PWM vs. MPPT

PWM, or Pulse-Width Modulation charge controllers are an older type of equipment that can be effective in very small, simple solar systems. They work by connecting and disconnecting to the battery rapidly, ensuring the battery voltage doesn’t go over its limit, but that means that much of the electricity that could be lost due to inefficiencies of the design.

These days, MPPT charge controllers are the only way to go. They can take input from solar panels a number of different voltages and make sure it’s converted in real-time to the exact voltage needed to charge the batteries.

How to size a charge controller

Sizing a charge controller can be a tricky balancing act between designing your solar panel array and designing your battery bank. Thankfully, the two best manufacturers of MPPT charge controllers have created software tools that can help you choose the exact right product for your system. Check them out here to choose an MPPT charge controller:

And the Outback Solar Sizing tool. You can click the link above or watch the video below to learn more about using the Outback solar array sizing tool:

Choosing an inverter:

Inverters take DC power from your panels and batteries and turn it into AC power that gets sent to your appliances via your main circuit breaker panel. For off-grid applications you use a similar appliance called an “inverter/charger.”

Inverter/chargers can take input power from both solar panels/batteries and the grid or an external generator, which means you can pull up at an RV park and plug in if you need more power for awhile, or if it’s particularly dark or cloudy and you need to charge your batteries.

To choose the right inverter/charger, you need to know something else about your appliances: the largest amount of power (in watts) you will need at any moment.

Some appliances, like laptops or DVD players, run at the same wattage all the time, while others, like refrigerators and vacuum cleaners, require extra power to start up. This extra power is called “Surge Power,” and it’s also measured in watts.

Inverters are rated in watts, and also provide a separate rating for surge power. To choose the right inverter for you, use the wattage from all the appliances you listed in step 1 above (wattage, not watt-hours), and choose an inverter that can handle that number.

Calculating surge power is kinda the same. First, add up the wattage requirements of all the non-surge appliances you might have running at the same time, then add the surge requirements of the others. Here’s an example of how that might work:

Electricity needs example:

Appliance

Continuous

Surge

Air Conditioner

2000

? 3,300

Refrigerator

180

? 600

Fan

40

? 120

Laptop

225

? 225

Lightbulbs

36

? 36

Radio

100

? 100

Total continuous: 2,581

Total surge: 4,381

In the example, you need an inverter that can handle 2,581 watts of continuous output. During times when every surge appliance is starting up, you’d still need the lights (36 watts), laptop (225 watts), and radio (100 watts) for 361 watts plus the refrigerator (600 watts), fan (120), and air conditioner (3,300) for 4,020 total watts of surge power, which equals 4,381 watts at once.

Choose an inverter that can handle both 2,581 watts continuously, and 4,381 watts at surge times. If your inverter is undersized for potential surges, you could end up with tripped breakers, fried wires, or worse.

Choosing a pre-wired system

Now that you know the size of inverter and charge controller you need, you can look at the options for pre-wired systems and choose one that has the correct components for your needs.

Each system’s main components are a charge controller and inverter. Choose the pre-wired panel that matches the needs you discovered in the last step.

Choosing wires:

Choosing the right wire sizes for a solar panel system is essential for safety and performance. Wires that are undersized can have problems with power loss and overheating. This is not something you want to screw up.

How power is like water

Electricity flows through wires kinda like water flows through pipes. Imagine a large-diameter hose. Water can flow though really quickly, and it’s easy for the hose to carry a lot of water at once. The same is true for wires; the larger the diameter of the wire, the less resistance to electricity flow there is.

Now think of a very long hose compared to a short one. The water needs extra energy to push it all the way through. For electrical wires, we call that difficulty “resistance,” and just like with hoses, smaller diameter more length means more resistance—except the extra energy here turns into heat.

Putting it all together: If your electrical wires are not large enough or if the cable is too long, the resistance is higher resulting in fewer watts going to either your battery bank or the grid. More specifically, as wire length increases, voltage decreases.

The takeaway: size matters

The lesson from the above example is simple: You want wires of a diameter that can handle the power you’re putting through them, and not longer than necessary. And when it is necessary to make longer wires, you need to increase their diameter to reduce the resistance and get your power where it needs to go.

Copper wires are sized using numbers defined by the American Wire Gauge (AWG) scale. The lower the gauge number, the less resistance the wire has and therefore the higher current it can handle safely.

Choosing wires

So now that you have the panels, the batteries, and the pre-wired inverter panel, which wires are left to buy? Here’s a list:

Wires from the solar panels to the charge controller

Wires from the inverter panel to the batteries

Wires to connect the batteries together

Wires from the inverter to your main breaker

Here’s how to choose the right sizes for each:

From the solar panels to the charge controller

Solar panels are all pretty standard. The come with cables attached, and it’s your job to wire them together in the right way and get that power to the charge controller. You need to choose wires of a size that won’t allow the voltage to decrease by more than 3% over the length of the wire.

To choose the right size wire, you need to first calculate a number called VDI (for Voltage Drop Index). Hey, at least it isn’t STD, right?

Here’s an example: Our Canadian Solar CS6K-27M 275-watt solar panels from above put out 8.8 Amps at 31.3 Volts. If we wire 4 panels in parallel, that’s 35.2 Amps at 31.3 Volts. We need to run the cables for 15 feet to get to our charge controller, and we’re shooting for a 2% voltage drop.

According to the table below, we see that our number of 11.25 could be rounded up to 12. For a VDI of 12, we need wires of AWG 6.

Wire Size

Area mm2

COPPER

ALUMINUM

AWG

VDI

Ampacity

VDI

Ampacity

16

1.31

1

10

Not Recommended

14

2.08

2

15

12

3.31

3

20

10

5.26

5

30

8

8.37

8

55

6

13.3

12

75

4

21.1

20

95

2

33.6

31

130

20

100

0

53.5

49

170

31

132

00

67.4

62

195

39

150

000

85.0

78

225

49

175

0000

107

99

260

62

205

From the inverter panels to the batteries

Wires from the inverter panel to the batteries are different than others. You don’t want to mess around with choosing wires that won’t be able to keep up with the demands of the inverter. Choose 2/0 or 4/0 gauge wires to connect your battery bank to the inverter.

To connect the batteries together

Similarly, don’t mess around with battery wire. For our example system, we’ll need 7 of these to connect the 8 6V batteries in series. Battery cable lengths are typically very short. We’d choose 13-inch 2/0 AWG cables to do the job.

Wires from the inverter to your main breaker

The job of the inverter is to convert the DC power from your panels and batteries into standard 120-volt AC power for use in your home. As such, a standard 120V AC cable can be used to connect the inverter to the AC panel serving your tiny home with power.

Chapter 5:
Buying solar equipment

Solarizing your tiny house will require parts and confidence! You can get the equipment from a supplier and either install it yourself or have an expert do it for you.

This chapter includes our favorite places to buy equipment and all the components we recommend:

Where to buy solar equipment:

Amazon – Amazon’s advantages are its popularity and free shipping benefits. You’re likely to find comprehensive user reviews for all the products you need, and even a good knowledge base spread among the answered questions for individual products. You might struggle to find the right information, and product support might be difficult to get.

altE Store – This vibrant online business is staffed by wise and knowledgeable folks, and offers complete solutions for your off-grid needs. You can count on them for expert help in choosing components, designing and building your system, and troubleshooting problems. Their helpful video knowledge center is a lifesaver if you need to understand more about the whole process of designing and building a solar panel system—on or off-grid.

Wholesalesolar.com – This 100% employee-owned company out of northern California has decades of experience in off-grid and residential solar power. Their sales reps are all knowledgeable solar experts who can help walk you through everything related to your solar project.

Solar Power Rocks Recommended Components for your tiny house:

If you’re ready to begin exploring components, take a look at our recommendations below. The best off-grid solar websites all offer kits that include most of what you need to begin and allow you to add batteries, inverters, and racks that fit your needs.

Or, you can piece together individual components to completely customize your system how you want it, and take advantage of special savings that might get you a better price than the pre-designed kits!

Tiny House Solar Kits

Alt-E Store’s 1.2-kW Tiny house off-grid solar kit ($6,000 out the door)
This complete kit includes everything you need to go solar on a tiny house, allowing you to choose battery and mounting options at the time of ordering. But the specified batteries might be undersized for your needs.

Missing: The batteries might be undersized for your needs – you can add more.

Wholesale Solar’s “The Cabin” 1.18-kW system ($6,300 before batteries)
This kit comes with almost everything you need, inclulding American-made Solar World panels. You’ll have to add on batteries, though, at the cost of about $2,000, and the whole kit is a bit more expensive for what you get.

Amazon’s Renogy 1.2-kW kit or EcoWorthy 1-kW system
These kits are great for small installations. Both are out together by Renogy, which is a newer player in the off-grid solar space. The price is right and the free Amazon shipping ain’t bad neither! Still, the kit is already old in the solar world, with lower-wattage panels that will take up more space.Missing:racks, Batteries, inverter.

Larger Off-Grid Solar Kits

Alt-E Store’s 5.4-kW Off-Grid home kit (around $19,000 out the door)
This complete kit includes everything you need to go solar on a standard residential house, depending on where you live. Happily, Alt-E Store provides a handy guide to how much power you can expect, and allows you to choose battery and mounting options at the time of ordering.

Missing: Nothing

Blue Pacific’s 5-kW Off-Grid house kit ($8,200)
This fine kit is designed by the experts at Blue Pacific to provide your home with all the power it needs. You’ll still need to choose batteries and racks to fit your needs.

Purchasing Individual components:

If you’re looking to fill in the gaps from one of the kits above, or if you’d like to avoid one-size-fits-all solutions and want to customize an installation for yourself, here’s a guide to everything you’ll need:

Solar Panels – Because you’re looking to power a tiny house, your best bet is to find the most efficient panels you can to squeeze every kilowatt-hour of solar energy out of the small roof over your head. There are still choices to be made! Here are our favorite panels, and what you might expect to pay for each:

Canadian Solar CS6K-275M 275-watt solar panel ($175) – Don’t let the name fool you: this panel is made in China, but it’s got quality to spare. It offers what is currently one of the lowest prices per watt of energy, and it’s high output is perfect for tiny house roofs.

Panasonic VBHN330SA16 330 Watt HIT High Efficiency Solar Panel ($357) – This is the Cadillac plan. If you want the best, here it is, complete with the best materials warranty in the world. These panels put out 20% more energy in the same space as the other panels in this list, and they work better in high-heat environments, too.

Mounting Racks – Not all mounting hardware is created equal, and the first hurdle is determining the best fit for your roof type. Here are our favorites:

For Metal Roofs: S-5! Products (~$200) – S-5! touts itself as the “Undisputed Leader in Metal Roof Attachment Solutions,” and we agree! If you have a metal roof on your tiny house, S-5! Products are the best choice to attach panels—often without penetrating the roof and exposing your tiny house to possible leaks!

For Composite/Asphalt roofs: IronRidge Solar Flashing and mounts (~$300) – Ironridge solar makes everything you need to easily attach panels to your roof. Their flashing slides under the shingle above it and seals water-tight, and their rails attach to the integrated mounts with just a bolt, making installation a snap and completely protecting your roof.

– Just like up on the roof, IronRidge products are the best way to get your panels mounted and aimed where they need to be.

Battery – Batteries are another animal entirely, because they’re either huge, heavy and difficult to care for (Flooded Lead Acid), or very expensive (lithium). Lithium batteries have improved by huge amounts in the last decade, but their cost is still not quite where it needs to be to make sense for every off-grid homeowner.

For Flooded Lead Acid (FLA) batteries: Trojan ($200-$400 per usable kWh) – Trojan batteries set the standard for solar+storage applications. They’re trusted by more off-grid experts than any other company. Still, if you’re going to go lead acid, be ready for 500-1,000 lbs. of batteries that take up a good chunk of space, and also be ready to maintain them on a regular basis. More on this in the construction process section below.

For Lithium batteries: SimpliPhi ($1,200-$1,400 per usable kWh) – Lithium batteries are more expensive; that’s just a fact. But check this comparison: You might need 55 ft² for 912 lbs. of FLA batteries, whereas you could get the same amount of energy storage in a lithium battery that weighs 49 lbs. And takes up 15 ft² of space. On top of that, lithium batteries require no maintenance and last twice as long. So maybe the expense is worth it to you.

Charge Controllers

A charge controller is one of the most important parts of your system. It determines how fast, how completely, and how sustainably your batteries get charged by your solar panels. We recommend MPPT charge controllers for what they can do, and there are a few companies that do them best:

MidNite Solar ($300-$700) – MidNite is a great American manufacturer of charge controllers. They’re flexible, reliable, and ultra-safe. The company offers the ability to start small with its 30 Amp “KID” controller, and add more KIDs as necessary as you grow your family of solar panels! If you’re ready to go big, MidNite’s classic 150 can put out as much as 96 Amps at 150 Volts.

OutBack Power Systems ($120-$550) – OutBack offers rugged and reliable products for tiny home use, starting as small as the truly tiny “Small Harvest” controller that can ensure you’re squeezing every drop of juice of out of those sweet panels on your roof. For more robust applications, OutBack’s Flexmax controllers can handle up to 7,500 watts of output and charge battery banks from 12 to 60 Volts.

Inverters

Inverters take DC power from your panels and batteries and turn it into AC power that gets sent to your appliances via your main circuit breaker panel. For off-grid applications we almost always recommend a similar appliance called an “inverter/charger.” Inverter/chargers can take input power from both solar panels/batteries and an external generator, which means you can pull up at an RV park and plug in if you need more power for a while, or if it’s particularly dark or cloudy and you need to charge your batteries. Here are our favorite manufacturers of inverter/chargers:

OutBack Power Systems ($1,600-$1,900) – Outback’s FXR series of inverter/chargers are perfect for off-grid applications using traditional appliances. The series comes in sizes between 2,000 and 3,600 watts, to handle enough power to run all the appliances in your tiny home or cabin, and automatically start up your backup generator when battery voltage is getting low.

Samlex EVO Series ($1,200-$1,600) – Samlex is an excellent alternative to the Outback models, and at a lower price point, it can help you save cost. A unique feature of the Samlex EVO series is the ability to hook a charge controller directly to the inverter, which helps reduce the amount of wiring necessary in a system without DC loads (like lights or DC appliances).

Wiring – The rest of your system consists of wiring that goes between all the components, and includes breaker switches and surge protectors to prevent bad things from happening. While you can piece together a solution from many companies’ parts, your best bet is to stick with a single company:

Again, with a pre-built inverter panel, you’ll only need to choose wires for the panels and battery system. When in doubt, follow pre-built kits for a list of components and ask a professional for advice.

Pre-Wired Inverter Panels – A pre-wired inverter panel makes off-grid solar as simple as connecting wires and entering settings for the inverter and charge controller. The amount of time saved by a pre-wired system is staggering. If you’re not an electrical wizard (maybe even if you are), we highly recommend the following panels:

Midnite Solar Pre-Wired System with Magnum Inverter ($4,000 for typical tiny house) – These systems take advantage of the Midnite Solar Classic Series Charge Controllers, which are by far our favorite solar product out there. They can be purchased complete or as a DIY kit. Make sure to choose the right size and voltage for your needs.

Outback FlexPower Pre-Wired Inverter Panels ($4,000 for typical tiny house) – If you’re looking to stick with one company for both charge controller and inverter, the Outback FlexPower panels can’t be beat. They make it dead simple to connect your components, and their documentation is second to none when it comes to making the final choices for your system. Again, choose the panel with the proper inverter wattage and battery system voltage (24 or 48) for your needs.

Glossary:
Important solar terms

Amp

A measurement of charge flowing through a circuit over a period of time.

Amp-hour

A measure of charge in batteries. A battery rated to store 100 amp-hours of charge can produce 100 amps of electric current for up to one hour at its rated voltage.

Charge Controller

A piece of equipment that manages the charging of batteries in a solar system. The charge controller receives energy from solar panels and passes them to the batteries to charge them.

Inverter

The Inverter (or Inverter/Charger in an off-grid system) is the piece of equipment responsible for taking energy from the solar panels and batteries and sending it to the main panel. Energy from the solar system is sent as Direct Current (DC), and converted by the Inverter to Alternating Current (AC).

Off-Grid

Disconnected from public utilities (i.e. water, sewer, electricity).

Voltage

The amount of potential energy between two points on a circuit. In

Watt

A watt is a measure of energy usage (or production). It is the product of the potential energy and the current flowing in a circuit (i.e. Watts = Volts x Amps)

Watt-hour

The measurement of the usage (or production of watts of electricity over time. For example, a solar panel rated to produce 100 watts under Standard Test Conditions exposed to direct sunlight for one hour will create 100 watt-hours of electricity. Conversely, a 100-watt lightbulb will consume 100 watt-hours of electricity if it is turned on for one hour.

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